I noticed that my 2023 return shows an amount on schedule 2 Line 13 when none of the forms I entered should have filled that line out. How do I amend this?

You would have to first determine why you reported uncollected social security/Medicare/Railroad retirement tax or had taxable group-term life insurance on which you didn't pay social security/Medicare tax.

The culprit would likely be your W-2 entry. The amount in box 4 should be 6.5% of the amount in box 3 for your social security tax. The amount in box 6 should be 1.45% of the Medicare wages reported in box 5. If you had group-term life insurance reported in box 12 on your W-2 form you would owe social security tax on that. 

In short, you would have to see if you entered your W-2 form correctly of if it correctly reported your wages and life insurance benefits in box 12. If the W-2 is wrong then the tax listed on line 13 of schedule 2 may be correct. If you entered the W-2 wrong, then you can amend the return and enter it correctly.